Regulation of hen granulosa cell prostaglandin production by transforming growth factors during follicular development: involvement of cyclooxygenase II.

Abstract

PGs are important physiological regulators of granulosa cell proliferation during ovarian follicular development. The rate-limiting step in the synthesis of PGs from arachidonic acid is catalyzed by cyclooxygenase (COX). Although two isoforms of COX (COX I and COX II) have been identified in the ovary, the nature and physiological significance of their regulation by transforming growth factor (TGF) alpha and TGF beta are unclear. The object of the present studies was to investigate the regulation of hen granulosa cell PG production by TGF alpha and TGF beta and the role of COX II in this process. Granulosa cells from the first (F1) and fifth and sixth (F5-F6) largest hen preovulatory follicles were cultured for up to 21 h in the presence of TGF alpha (0-10 ng/ml) and/or TGF beta (0-20 ng/ml). COX protein and messenger RNA (mRNA) levels were determined by Western blot and Northern analysis, respectively. Granulosa cell PGF and PGE secretion was increased by TGF alpha but suppressed by TGF beta in vitro. The increase in PG secretion was accompanied by an elevation of COX II content, which was dose and time dependent, with maximum response observed within 6-12 h. Maximal increase in COX II mRNA abundance was evident at 4 and 8 h in cells from F1 and F5-F6, respectively. Although TGF alpha-stimulated PG secretion was higher in cells from mature follicle (F1), the magnitude of change in COX II mRNA abundance and protein content was, however, not dependent on follicular maturation. TGF beta significantly suppressed basal and TGF alpha-induced COX II transcript levels. COX I transcript, however, was undetectable irrespective of the presence of TGF alpha, duration of culture or the stage of follicular development. In conclusion, the mitogenic response of granulosa cells to TGF alpha is mediated by changes in PG secretion, which are regulated at the level of COX II. Unlike the control of PG secretion, the regulation of COX II by TGF alpha is independent of follicular maturation. Whereas COX II may be important in the signaling cascade for TGF alpha in the regulation of granulosa cell proliferation, the mechanism(s) of regulation of follicular stage-dependent PG secretion by the growth factor is complex and requires further investigation.